A number of approaches have been suggested in the prior art for creating a nuclear magnetic resonance gyroscope. In general, they use a nuclear magnetic resonance controlled oscillator. Rotational information is derived from the phases of the nuclear moment Larmor precession signals by phase comparison and magnetic field control circuits.
Such devices have significant problems which limit their use. For instance, some devices are limited by the relatively short relaxation times of the gases which they use. Also, typical strong direct coupling between the gases and the light, which is used for magnetic moment alignment or magnetic moment detection, limits both the relaxation times and the signal-to-noise ratio, and therefore limits usefulness of such instruments.
In a known type of gyro, the gyro bias polarity is reversed when the drive and sense axes are interchanged. This particular class of gyro is identified as Class II Coriolis Vibratory Gyro and is characterized by being inherently counterbalanced, symmetrical about the input axis and having orthogonal degenerate vibration modes. Self calibration of the gyro bias is achieved by employing two gyros to measure the angular rate and sequentially reversing the gyro bias. The sequence of data from the gyros may be processed in an algorithm to solve for the gyro biases and subtract them from the measured rate. The two self-calibrated gyro angular rate measurements are averaged to reduce the angle random walk.
Self-calibration of a gyro bias under dynamic operating conditions requires the simultaneous measurement of angular rate by, for example, a pair of Class II Coriolis Vibratory Gyros (CVG) or a single gyro with dual sensing elements. Class II CVGs have the ability to reverse polarity of the gyro bias by interchanging their drive and sense modes. An algorithm solves a set of four equations to estimate the gyro bias and subtract it from the measured angular rate. A Dual Resonator Gyro (DRG) may facilitate this simultaneous measurement of angular rate by a pair of gyros. System simulations have shown that the contribution of gyro bias uncertainty to the growth of position error of an inertial navigation system can be reduced by nearly three orders of magnitude using self calibration of gyro bias.
Gyro scale factor uncertainty is another source of error in inertial systems. The contribution to position error due to scale factor uncertainty is dependent on the magnitude of the angular rate experienced. Compensating for gyro scale factor uncertainty would further improve the performance of inertial navigation system.
There is a need in the art for improved self-calibrating nuclear magnetic resonance gyros.